Twist-drill.



PATENTED JULY 17, 1906.

E. (3.1 PECK. TWIST DRIL.

APPLIGATION HLBD MAR s 190e NITEI) STATES .PATENT OFFICE.

EUGENE C. PECK, CE CLEVELAND, CHIo,'AssI.CNoR To THE CLEVELAND y TwisrDEiLL COMPANY, CE CLEVELAND, omo, A CoRPCEArioNoE OHIO- TWIST-DRILL.

Patented July 17, 190e.

kApplication led March 9, 1906. Serial No. 305.023. Substituted for abandoned application led June 3, 1905, Serial No. 263,516.y

To @ZZ whom tdw/bay concern:

Be it 4known that I, EUGENE C. PECK, a citizen of the United States, residing at Cleveland, in the county kof Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Twist-Drills, of which the following is a full, clear, and exact description.

This invention relates to twist-drills, and has for its object the production of a drill having a greater cutting capacity than the ordinary drill and possessing the same strength.

Heretofore in tools of the class to which my invention relates the spiral grooves have been of such form that the cutting efiiciency of the tool diminishes more and more as the drill is worn away by repeated sharpening. This arises from ,the fact that twist-drills must be provided with a web constantly increasing in thickness toward the shank, and Ilo construction or method of formation has heretofore been devised by which this increase in thickness could be obtained without also changing the contour of the groove from the point toward the shank. The method of increasing the web has been merely to retract the milling-cutter in a line lying in the plane of rotation. It is plain, however, that the simple withdrawal of the .cutter in this fashion from the blank would make the groove shallower, and thus afford less chip space. Therefore, to compensate for the shallowness of the groove a skew'cut has been made, either by shifting the millingcutter so that its axis yforms a different angle with the axis of the blank or by increasing the pitch `of the helix toward the shank. Each of these expedients will, as is well known to those skilled in the art, give a skew cut, increasing the width of the groove between the lands, but simultaneously altering the contour of the groove. This alteration of the contour is, however, highly undesirable, .as the cutting edge will no longer be a straight lip and will become more and more hooked as the shank is approached; but it has not hitherto been avoided.

I have .discovered a method of making the groove by which the web can be increased in thickness toward the shank and the groove maintained of practically constant chipspace without altering the contour so as to lose the straight cutting-lip. Further, `my

upper face of the cutting-lips and the plane normal to the axis at the point. The drills hitherto produced have had a positive angle' along the entire width of the cutting edge at the point, but they have not maintained this angle along their entire width .throughout the length of the flutes, ythe inner end bf the cutting edge having absolutely no inclination or dip as ,the shank is approached.

Referring to the accompanyin drawings, Figure 1 is a side view of my dril a millingcutter being shown in position in full lines as it is in the beginnin of thecutting operation and shown in dotted lines as it is at the .close, still maintaining the same Aangle between its plane of cut-and the axis of the blank. Fig,

' 2 is an end View of a blank, showing the milling-cutters in position. Fig. 3 is an end view of the drill, showing it pointed and clearance given for the cutting edges. Fig. 4 is an end view of the drill, taken when worn to the line 4 4 of Fig. 1, the -drill being, properly pointed and given clearance. Fig. `5 shows Fig. 4 superposed on Fig. 3, the dotted lines illustrating the comparative position of the grooves at the point of the drill, `the'full lines showing their position near the'shank. Fig. 6 is a fragmentary axial section taken near the shank, showing the dip orv positive angle behind the inner end of the cutting-lip. Fig. 7 is a view precisely similar to Fig. 4, dotted lines being added to illustrate the frrmation ofa positive angle for the` cutting e ge.

In the formation of the .drill the millingcutters A A, diagraphically illustrated, are placed at the proper angle at .the beginningof the operation, as shown in Fig. 2. The part of the grooves cut -by the sides A, having the curve of the lar er radius, will have when the drill is proper ypointed a straight v lip B extending from the outer end to and past the cutting-corners B B', so called the art, which corners mark the inner end o f the actual cutting portion of the straight lip. These cutting-corners are at the intersection of the cutting-lips B and the index-line y.or dead edge C, produced by the intersectionof yIOO the plane surfaces D D, which are ground off to give clearance behind the cutting edges.

The index-line or dead edge at the point of a drill, as is well known, meets the straight lips at an obtuse angle, and by consequence it will be readily seen that that portion E of each lip extending between the corner and the bottom F of the groove will be of less radius than the corner B/ itself, a matter of importance, as will appear fully below. AThis structure at the point of a drill is old; but in all cases where the web has been thickened toward the shank and the skew cut given the straight-line portion of the cutting-lip has of course become shorter and no longer extended past or even to the cutting-corner and has eventually resolved itself into a hook meeting the index-line at about a ri ht angle -and leaving it at substantially t e same angle, In order that this straight line of the cutting edge may be preserved throughout the length of the drill, I do not skew the milling-cutters or change the pitch of the helix as I withdraw the cutters for the purpose of thickening the web, but maintain the same angle of cut throughout the length of thev fluted portion.

Furthermore, instead of withdrawing the milling-cutters away from the axis of the blank in a direction lying in the plane of their cut I move them away each in a direction at an angle to the plane of the cut somewhat as indicated by the line Z Z in Fig. 5, in which iigure the diameter X X is` normal to the planes of cut.

As will be apparent from a study of Fig. 5, the movement of the cutters in the line indicated thickens the web and makes the groove shallower by reason of the innermost part of the grooves moving away from the axis of the blank; but at the same time the chipspace will bemaintained practically the same, since the forward portion of the milling-cutter will, due to the direction of advance, obviously out into the blank to an amount amply sufhcient to compensate for the extra metal left behind the rear portion. Thus it is possible to thicken the web of the drill toward the shank and preserve the straight edge of the cutting-lip without material loss of chipspace. AS a further consequence of this method of formin the drill it will be seen that the continua advance of the millingcutters as indicated will so form the flutes that a positive cutting angle will be maintained along the entire width of the edge throughout the len th of fluted portion ofthe drill, as will be set orth below.

It is evident from consideration of the fact that the line of the cutting edge continues past its cutting-corner B, and therefore nearer to the axis G, and 'the fact that the twist of the roove will as it advances up the drill throw t ese inner portions E, having the smaller radii, behind the cutting-corner B in its axial plane thata projection of the innermost part of the groove would follow the dotted line in Fig. 7. This of course produces a dip behind the entire cutting edge B, which cutting edge is, as above pointed out, comprised in that portion of the lip between the outer end and the cutting-corner. For example, in Fig. 6 the axial section taken through the cutting-corner B shows the dipy behind the corner. The dotted line II is normal to the axis of the drill, and the dotted line I is parallel to the axis. The dip of the surface of the cutting-face of the groove immediately behind the cuttingcorner is clearly illustrated. Thus a positive angle of less than ninety degrees is presented along the entire width of the edge B, even at the inner end B. In the prior art, however, as the milling-cutters are withdrawn to thicken the web and a skew cut made to compensate therefor the straight edge of the cuttin -lip lip extending past the cuttin -corner will soon no longer have a less ra ius than the corner itself, with the consequence that there will be no dip behind the cutting edge at the corner and the angle presented by the surface of the groove behind the inner end of the cutting edge will be ninety degrees or more. This feature of my drill is broadly new in combination with a substantially constant chip-space.

Referring again to Fig. 5, it will be seen that as the cutter is advanced along the line indicated, although all parts of the cutter itself are of course advanced a like amount, the extreme inner or bottom art F of the groove advances more rapidly t an the lands K K', which form the boundary of the groove. This arises from the fact that the foremost portions of the advancing side of the cutter pass out of the circumference of the blank during the advance. This causes the forward boundary K of the groove to lag circumferentially. Similarly the rear boundary lags by reason of the advance of the milling-cutter, causing the more rearward portions of the cutter to enter the metal. The result of this 'is that the innermost part orbottom F of the groove is of a pitch dierent from that of the substantially parallel edges K K of the groove and approaches nearer to the land K as the groove itself approaches the shank.

From the above it will be evident that I have vsucceeded in producing a drill which has a web of constantly-increasing thickness and which preserves a straight cutting edge from the point to the shank and in which the chip area of the groove is not substantially diminished. Further, I have produced a drill of such form that the surface of the groove behind the cutting-corner presents a positive ycutting angle of less than ninety degrees to the material at all points along the cutting edge throughout the entire length lof the groove.

disappears into a curve and the portion o the IOO I-Iaving thus described my invention, I claim 1. A twist-drill havin a helical groove and a 'Web of increasing thic mess from the point toward the shank, and having a cutting edge Whose up er surface forms less than a right angle with the plane of the work, substantially throughout the length of the grooved portion.

2. A twist-drill having a helical groove and a Web of increasing thickness so formed as to present at every point throughout its grooved ortion a substantially straight cutting-lip avin a positive cutting angle.

3.A twist-drill having a helical groove and a Web increasing in thickness from the point toward the shank, said roove being so formed that the bottom 0I the groove approaches nearer to one edge than the other, toward the shank, whereby the proper cutting-lip and chip-space are maintained.

4. A twist-drill havin a helical groove and a Web of increasing thicIiness from the point toward the shank, said groove being of substantially constant chip-space throughout and formed to present a cutting-lip of less than a right angle Wherever pointed.

5. A twist-drill havin a helical groove and a Web of increasing thic mess from the point toward the shank, said groove having substantially constant chip-space throughout and having a substantially straight cuttinglip Wherever pointed.

6. A twist-drill having a helical groove and a Web of increasing thickness from the point toward the shank, the edges of said groove being substantially parallel and the extreme bottom of said groove being of a pitch dii"- ferent from that of said edges.

In testimony whereof I hereunto aiiX my signature in the presence of tWo Witnesses.

EUGENE C. PECK. 

